The present invention relates to a piezoelectric transformer; and, more particularly, to a laminated piezoelectric transformer for use in a converter and an adaptor.
Piezoelectric transformers feature smaller sizes and easily obtainable higher efficiencies than conventional electromagnetic transformers. For such reasons, piezoelectric transformers are gaining popularity as step-up transformers, e.g., backlight power sources of liquid crystal display (LCD) monitors. However, step-down transformers are more frequently used in power supplies than step-up transformers.
It is preferable that a piezoelectric transformer have such characteristics as high output power, less heat generation, small size and high efficiency. However, increasing the output power of a conventional piezoelectric transformer gives rise to the increased heat generation, which in turn reduces the output power thereof. The output power P of the piezoelectric transformer is represented as follows:   P  ∝                    k        2                    1        -                  k          2                      ·    V    ·          v      2      
where k is an electromechanical coupling coefficient of a secondary part of the piezoelectric transformer, xcexd is a propagation velocity of a mechanical vibration and V is the volume of the secondary part. If the temperature of the secondary part is increased due to the increased heat generation, the electromechanical coupling coefficient k of the secondary part decreases and the output power P also decreases accordingly.
It is, therefore, a primary object of the present invention to provide a piezoelectric transformer capable of generating a high output power by suppressing heat generation therefrom.
In accordance with a preferred embodiment of the present invention, there is provided a piezoelectric transformer including:
an output part having laminated sheets of a first piezoelectric material; and
one or more input parts, each having laminated sheets of a second piezoelectric material, wherein a piezoelectric strain constant of the second piezoelectric material is greater than that of the first piezoelectric material.
In accordance with another preferred embodiment of the present invention, there is provided a piezoelectric transformer including:
a laminated body having an output part and one or more input parts; and
external electrodes,
wherein the output part includes sheets formed of a first piezoelectric material and first internal electrodes, each of the first internal electrodes being formed between every two neighboring sheets of the first piezoelectric material and the first internal electrodes being alternately exposed at first two substantially opposite sides of the laminated body and
wherein each of the input parts includes sheets formed of a second piezoelectric material and second internal electrodes, each of the second internal electrodes is formed between every two neighboring sheets of the second piezoelectric material and the second internal electrodes are alternately exposed at second two substantially opposite sides of the laminated body, and
wherein the external electrodes are separated from each other and formed on first and second side surfaces, and
wherein a piezoelectric strain constant of the second piezoelectric material is greater than that of the first piezoelectric material.